CDMA (Code Division Multiple Access) radio systems employ two types of power control, uplink power control and downlink power control. The uplink power control solves what is known as the near-far effect, i.e. a situation in which the transmission of a user equipment located far from the base station fades under the transmission of a user equipment near the base station if no power control is used.
The present invention relates to downlink power control, where power control is needed to reduce multiuser interference, or to reduce interference caused to other cells, and to compensate the interference caused by other cells.
For example, IS-95 radio system uses slow power control. The system is mainly intended for speech transmission. The base station periodically reduces the power control employed. A user equipment measures a frame error ratio and when the frame error ratio exceeds a predetermined limit, for example one percent, the user equipment requests for more transmission power from the base station. The power control is carried out at approximately 15 to 20 millisecond intervals (the frequency being 50 to 67 Hz), and the dynamic power control range is plus/minus six decibels.
More recent CDMA systems, such as the cdma2000 system or the WCDMA system, also use fast power control, and the power control can be carried out individually for each slot of the frame, and the dynamic power control range is fairly large. The frequency of fast power control is, for example, 800 Hz or 1600 Hz.
In recent mobile systems data is transferred in addition to speech, but the power control is not optimized in any way according to the requirements the services to be transferred set for the power control.